This application relates to an elevator car having lateral suspension provided by electromagnets mounted on the car and a car follower to create a repulsive magnetic force. Preferably, the car follower has a pair of electromagnets which are interconnected to move together.
Elevator cars are typically guided for movement upwardly and downwardly by passive suspension systems including spring biased rollers moving along rails. One challenge faced by elevator designers is the control of lateral vibration. Any vibrations that occur as the car moves laterally reduce the ride quality, which is undesirable.
One problem with addressing lateral vibrations is that the vibrations occur across a range of frequencies. Fully addressing these vibrations is not possible with typical passive suspension systems. In particular, to address low frequency vibration, a high spring stiffness for the passive suspension would be necessary. On the other hand, a high spring stiffness would not address the high frequency vibration, which would require a lower spring stiffness. Thus, passive suspension systems have not been able to address a wide band of vibration frequencies.
It has been proposed to utilize magnetic suspension members in combination with these passive suspensions. These combined systems have not always been fully acceptable either. Moreover, these systems have a resultant noise which would be undesirable.
Other suspensions rely solely upon magnetic suspension elements. These suspension elements have typically used an attractive magnetic force. That is, a steel rail is provided, and an electromagnet is provided on the car. The electromagnet is attracted to the steel rail. An electromagnet and guide rail are associated with each side of the car. Thus, in an idealized situation, two opposed attractive forces center the car between the two rails. However, in practice, this system would actually be unstable. Should the car move slightly toward either side, which would be the natural effect of an additional lateral force, then the system would become quickly unstable. In particular, the attractive force between the rail and the electromagnet is proportional to the inverse of the square of the distance. As the car moves closer to one of the two rails, the attractive force would also increase. Thus, should the car move closer to one rail, the attractive force pulling the car further toward that rail would also begin to overcome the attractive force pulling the car toward the other rail. One other problem with this type of system is poor controllability. There could be a good deal of power loss in the steel rail, and current saturation. Further, the shape of the rail would make controllability difficult.
A system disclosed in U.S. Pat. No. 6,510,925 would rely upon repulsive magnetic forces. A repulsive magnetic force would have the opposite correction to an attractive magnetic force, and would thus tend to center a car.
The system disclosed in U.S. Pat. No. 6,510,925 has a separate car follower associated with each of the two guide rails. These car followers are connected through springs to the car. Thus, the car followers are not free to move relative to the car, and are each independent of the other. These facts would make it more difficult to control the lateral vibration, and could, in fact, cause additional lateral and even vertical vibrations.